Precision analytical pump

ABSTRACT

Precision Analytical Pump of continuous flow, programmable and without pulsation, moves liquids and solutions without dead recharge time, for application in instrumental chemical analysis, in pharmaceutical and Fine Chemistry process lines. It consists of a micro-step electric motor ( 1 ), who drives a shaft with linear displacement ( 2 ), coupled to two pistons ( 3 ), which penetrate two volumetric chambers of variable volume ( 4 ), with antechambers ( 5 ) arranged between said chambers and motor, involving the movement path of pistons. Said chambers have connections with valves ( 6 ) for directional flow control and inner walls fit pistons with sealing rings ( 7 ). Said antechambers communicate in order inner saturated air can go from one to the other, for pressure equilibrium during pistons displacement. A digital electronic circuit monitors pump operation, limiting pistons course by sensors ( 8 ), and allows interface with the operator and with a computer.

SUMMARY

“ANALITICAL PRECISION PUMP”, with continuous flow, programmable and pulseless, moving liquids and solutions, without recharge dead time, for use in instrumental chemical analysis (Titration, continuous flow analyzers, low pressure liquid chromatographs, mass spectrometers); in process lines of pharmaceuticals products and Fine Chemistry; in clinics and hospitals for controlled infusion of medicaments. It comprises a micro-step electric motor (1), which drives a tubular shaft with linear displacement (2), coupled to two diametrically opposite pistons (3), which penetrate two volumetric chambers with variable volume (4), symmetrically opposed and coaxial to said axis, with antechambers (5), arranged between these chambers and the motor, involving the movement region of said piston. These cameras are equipped with connections for valves (6) of directional control flow. Chambers inner wall is adjusted by piston sealing rings (7). Said axis, cast in the length direction, allows communication between antechambers. A digital electronic circuit monitors pump operation, limits pistons displacement, by sensors (8) and communicates with the operator through keypad and LCD display, and a computer, through a serial port.

This patent request concerns to a precision pump for liquids, that can be used for analytical instrumentation, among other applications, implementing the innovative concept of opposite and coaxial volumetric chambers with pistons driven by a linear actuator, combining the traditional advantages of precision pumps to the innovative features of an instrument that can be used without the operational constraints found in conventional equipment.

Positive displacement pumps dispense volumes with accuracy better than 1% regardless of supply pressure. The challenges are: control of the variable geometry cavity dimensions, seals efficiency, contact surfaces durability, dead volume reduction, pulse elimination and recharge time. They are used in laboratory applications, analysis and synthesis, and industrial processes where flow rates and accurate volumes of fluids are required. The movement of fluid is caused by mechanical action of impulsion agent, which forces fluid, by compression, occupying and vacating variable geometry cavities in the same direction of the force transmitted to it. Pumps may be alternative (piston, diaphragm, membrane) or rotary (gears, lobes, vanes, helical screws, bolts, peristaltic).

Diaphragm pumps pulse a flexible membrane which constitutes one side of the variable volume chamber, displacing liquid with each movement, with pulsed flow. They may be solenoid driven or by mechanical or hydraulic means, and flow direction is controlled by directional valves. Piston pumps [2] operate by reciprocating motion of a piston in a cylinder, usually endowed with directional valves, and pulsating flow is attenuated by elastic shock absorbers and/or switching between various pistons. With precision and repeatability, they are used when high pressures are required, as in liquid chromatographs, HPLC type, and with typical flow rates ranging from 0.04 to 1.3 L/min, reaching pressures up to 345 bar, with many options of control and automation, as manual, analog, computer assisted or PLC, via RS-232.

Peristaltic pumps [3] compress one or more pipes in the direction of fluid movement by means of rollers or movable rods in continuous operation with simultaneous loading and unloading. They can reach flows from 0.6 to 45 L/min and pressures from 2 to 8.6 bars, with precision between 1 and 3%, and can be operated manually or assisted by computer or PLC. Peristaltic pumps are expensive and require constant pipes maintenance. They are the most used pumps for handling solutions in flow injection analysis system (FIA) [4,5], wherein rapid introduction of sample in the carrier solution flow, directed to meet other confluent reagent(s), generates transient signals in an on-line detector. Some detectors are sensitive to flow, in which case pulsation caused by switching between rollers (or fingers) of commonly used peristaltic pumps becomes limiting. Pulses generate baseline noise, as in miniaturized systems with electrochemical detection and μFIA, that receive buffers to reduce interference.

Syringe pumps [6] operate between 1 and 150 mL/min, with optimum repeatability and accuracy better than 0.1%, at pressures up to 200 bar, with options of manual control, analog, by computer or PLC. They provide constant flow rates or programmed gradients without pulsation, but with frequent interruptions for recharging. They are used in titrators, liquid chromatographs, mass spectrometers and dispensers, for the introduction of precise volumes of samples and reagents, while the pharmaceutical industry and the Fine Chemicals employ them in micro-reactors and dispensing process lines.

Automatic Titrators are widely used in chemical and clinical laboratories for routine analysis. Titration [7] is a procedure for quantitative determination of a chemical species in solution, by adding a known concentration of reagent in reaction of reproducible stoichiometry.

Liquid Chromatography [8] exploits differential migration of the components of a sample by multi-step chemical-physical equilibrium between a liquid mobile phase and a stationary phase, which may be liquid, supported by a finely divided solid, or solid, in the same condition. The mobile phase may be pumped under low pressure (LPLC), typically less than 13 bar, and high pressure (HPLC), up to 400 bar. The LPLC is widespread used in biomolecular research, such as studies of proteins and monoclonal antibodies, where high pressures would damage the analytes. It is common to use syringe pumps in LPLC systems, due to the absence of pulsations.

Supercritical Fluid Chromatography (SFC) [9] is an intermediate technique between Liquid and Gas Chromatography, where the mobile phase is a gas (usually CO2) heated to temperatures above its critical temperature and compressed to pressure above its critical pressure, simultaneously, becoming a fluid having differentiated properties from the gas and liquid phases. The SFC is applied to thermally unstable samples, with high molecular weight, allowing efficient and rapid separations. Supercritical chromatographs are similar to liquids and, usually, a suitable syringe pump at higher pressures replaces the alternating piston.

Syringe pumps can operate with disposables syringes, tubes and connections and, so, clinics and hospitals use them as standard equipment for drugs infusion into bloodstream of patients. Their disadvantages are the need to interrupt flow for refilling, the large liquid volume required for washing, when it is not used disposable material, and wear of contact surfaces by abrasion.

Micro step motors, assisted by specific drivers, are manufactured in different sizes and powers, and linear displacement provides high power to small motors with little weight, precise movements and good repeatability, does not generate pulsation and eliminates mechanical conversion mechanisms (rotation/translation), power loss and backlash, that compromises the accuracy [10].

The proposed product is a precision pump that comprises a linear actuator with micro-step motor (1), with a shaft (2) with braked rotation, in whose ends are connected two coaxial pistons (3), which penetrate two volumetric chambers (4) without direct contact with the inner walls thereof, with a watertight sealing rings (7), and reciprocating linear movement controlled by position sensors (8). Pumped fluids access the chambers by means of connections with flexible tubing and directional control valves (6). In a preferred construction, two antechambers (5), interconnected by internal duct axis, are arranged along the travel of the piston, covering the entire length thereof between the chambers and the motor. The shaft that drives the pistons may be the motor shaft itself or mounted in parallel thereto.

The adoption of opposite and symmetrical chambers, operated by common axis, allows filling one chamber while the other is evacuated, eliminating the dead time of recharging and the required brake, which compromise some applications, precisely those of higher precision pumps. The use of inert valve, without dead volumes and fast response, allows reversing the direction of pistons movement, between motor's steps, without changing the flow of the pumped liquid.

Communication between antechambers has the objective of transferring the saturated internal atmosphere reciprocally, in accordance with pressure variation caused by the recoil of a piston and the advance of the other, in order to balance internal pressure without gas exchange with the atmosphere, preventing drying of wettable surfaces, which prevents the formation of micro-crystals of nonvolatile solute and consequent abrasion, causing surface scratches and loss of tightness.

Pistons and chambers can be made of various materials compatible with the fluid, especially inert polymers, metal coated with PTFE, ceramic materials and calibrated glass, always taking into account the expected operating pressures. The minimum distance between movable walls without direct contact, eliminates friction, ensure parts longevity and preserves surface treatments. Horizontal arrangement places chambers access connections vertically upwards, turning automatic the elimination of air bubbles, difficult to remove from conventional pumps.

Reduced gap between pistons and chambers inner walls, and positioning of valves connections (together with sealing rings, in the construction with antechambers) forces the fluid to pass across the lateral extent of the wettable surfaces to arrive or leave chamber's end, where it is generated variation in volume. This fact allows reducing volume of liquid consumed for washing the pump, unlike conventional systems, which require the repetition of the complete filling, or disassembly.

FIG. 1 shows a preferred construction, applicable to pumps whose operation demand frequent changes of pumped liquid and repeated washings.

FIG. 2 illustrates a second preferred construction, applicable to dedicated operation, without requiring frequent washings, without antechambers, more compact and capable of be mounted strategically at the top of the bottle reservoir. Volume of chamber located between piston and motor is sealed and has the same functionality of the antechamber.

A digital electronic circuit controls valves and motor through a specific driver. Pressure and temperature sensors can be installed, preferably together with the access chamber connections. A membrane keypad and a LCD display are the user interfaces. It is provided a serial communication facility to command the device from the computer.

BIBLIOGRAPIC REFERENCES CONSULTED

1. Goldschmidtböing, F. et al, J. Micromech. Microeng., 2005, 15 673.

2. Snyder, L. R., Kirkland, J. J., Dolan, J. W., Introduction to Modern Liquid Chromatography, New York: John Wiley & Sons, 3^(rd) ed., 2009.

3. Smith, J. P. and Hinson-Smith, V., Anal. Chem., 2002, 74 (13) 385 A-388 A.

4. Trojanowicz, M., Flow Injection Analysis. Instrumentation and Applications, World Scientific Publishing, Singapore, 2000.

5. Trojanowicz, M., editor, Advances in Flow Analysis, Weinheim: Wiley VCH Verlag GmbH & Co., 2008.

6. Webster, J. G., Medical Instrumentation Application and Design, New York: John Wiley & Sons, 3^(rd) ed., 1998.

7. Holler, F. J., Skoog, D. A. e Crouch, S. R., Princípios de Análise Instrumental, Porto Alegre: Bookman, 6a ed., 2009.

8. Collins, C. H. et alii, Fundamentos de Cromatografia, Campinas: Editora da Unicamp, 2006.

9. Carrilho, E., Tavares, M. C. H., e Langas, F. M., Quim. Nova, 2003, 26 687-693.

10. Hughes, A., Electric Motors and Drives: Fundamentals, Types and Applications, Oxford: Elsevier, 3^(rd) ed., 2006. 

1) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting two symmetrical and coaxial opposing pistons (3), driven by common axis with alternating linear movement (2). 2) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claim 1, two volumetric chambers of variable volume (4), opposed, symmetrical and coaxial. 3) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claim 1, tubular antechambers (5), adjacent to said chambers. 4) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claim 1, a linear actuator constituted by electric microstepping motor (1) which moves the said axis. 5) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claim 1, directional valves (6) to control liquid input and output of said chambers. 6) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claims 1 and 2, communication between said antechambers. 7) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claims 1 and 6, communication through the channel passing inside the said axis. 8) “ANALITICAL PRECISION PUMP”, instrument for propulsion of liquids, particularly applicable to analytical instrumentation, chemical and pharmaceutical industrial process control and outpatient infusion, characterized by the fact of presenting, in conformity with claims 1 and 6, communication by external duct to said antechambers. 